OBJECTIVE: Examine polysubstance use (polySU) profiles and associated demographic, treatment, functioning, and mental health correlates among young people at alcohol and other drug (AOD) treatment entry.

METHOD:  = 2,094 young people (12-25 years) enrolled in AOD treatment between (mean age = 20.67,  = 3.42; 54% men). PolySU was modeled using latent profile analyses informed by severity of tobacco, alcohol, amphetamine, cannabis, opiate, MDMA, sedative, and cocaine use.

RESULTS: Three polySU profiles were identified: (1) extended-range polySU ( = 141; 7%); (2) high-risk opiate use with extended-range polySU ( = 160; 8%); and (3) moderate-range polySU ( = 1,793; 85%). Participants in the high-risk opiate use with extended-range polySU profile were most likely to be unemployed and not studying, homeless, at risk of eviction and hospitalized in the four weeks preceding AOD treatment enrollment, and have depression, anxiety, PTSD, and psychosis. Participants in the two extended-range polySU profiles were more likely to be enrolled in residential AOD treatment and to have been violent toward others in the four weeks preceding treatment enrollment, than participants in the moderate-range polySU profile.

CONCLUSIONS: PolySU was pervasive among young people entering AOD treatment. Clients in the most severe polySU profile experienced poorest functioning and highest rates of co-occurring mental health problems.